This invention relates to continuous-type ink jet printing systems, which create printed matter by selective charging, deflecting, and catching drops produced by one or more rows of continuously flowing ink jets. The jets themselves are produced by forcing ink under pressure through an array of orifices in an orifice plate. The jets are stimulated to break up into a stream of uniformly sized and regularly spaced droplets. The approach for printing with these droplet streams is to selectively charge and deflect certain drops from their normal trajectories.
A charge plate accomplishes droplet charging. The charge plate has a series of charging electrodes located equidistantly along one or more straight lines. Each charging electrodes is formed with an electrically conductive material. Electrical leads are connected to each such charge electrode, and the electrical leads in turn are activated selectively by an appropriate data processing system.
U.S. Pat. No. 4,636,808, which issued to Herron, describes a simple arrangement of the drop generator and the charge plate, but the orifice plate attached to the drop generator and the charge electrodes require careful mechanical alignment and fixation so that the charge electrodes align exactly with corresponding jets issuing from the orifice plate. If the jets are misaligned or become misaligned in use, the quality of printing is adversely affected. Misalignment of as little as 10 micrometers can cause rejection of the print head and require it to be refurbished. Matching of the dimensions of the ink jet array and the charge electrode array becomes problematic, especially for page-wide arrays where there are thousands of ink jets and charge electrodes.
Conventional and well-known processes for making the orifice plate and charge plate separately consist of photolithography and nickel electroforming. Orifice plate fabrication methods are disclosed in U.S. Pat. No. 4,374,707; No. 4,678,680; and No. 4,184,925. The commonality of these and other patents is in the deposition of a nonconductive thin disk onto a substrate, which is followed by partial coverage of this with nickel to form an orifice. In the prior art process, a conductive substrate of solid metal is used to hold the thin disk and the plating. After formation of the orifice, the metal substrate is selectively etched away leaving the orifice plate electroform as a single component. Charge plate electroforming is described in U.S. Pat. No. 4,560,991 and No. 5,512,117. These charge plates are made by depositing nonconductive traces on a metal substrate followed by deposition of nickel in a similar fashion to orifice plate fabrication, except that parallel lines of metal are formed instead of orifices.
Accordingly, it is an object of the present invention to provide a simplified and more accurate method for fabrication of the orifice plate and charge plate. It is another object of the present invention to provide such an aligned orifice plate and charge plate as one, self-aligned component.